U.S. patent application number 17/434704 was filed with the patent office on 2022-06-02 for method for authenticating a magnetically induced mark with a portable device.
The applicant listed for this patent is SICPA HOLDING SA. Invention is credited to Andrea CALLEGARI, Claude-Alain DESPLAND, Todor DINOEV, Jean-Luc DORIER, Edmund HALASZ, Evgeny LOGINOV.
Application Number | 20220171953 17/434704 |
Document ID | / |
Family ID | |
Filed Date | 2022-06-02 |
United States Patent
Application |
20220171953 |
Kind Code |
A1 |
DINOEV; Todor ; et
al. |
June 2, 2022 |
METHOD FOR AUTHENTICATING A MAGNETICALLY INDUCED MARK WITH A
PORTABLE DEVICE
Abstract
The invention relates to a method of authenticating a
magnetically induced mark applied on a substrate including
magnetically oriented partially reflective platelet-shaped magnetic
or magnetizable pigment particles, with a portable device equipped
with a light source operable to deliver visible light, an imager, a
processor and a memory, the method comprising calculating, with the
processor, a corresponding average intensity I of the light
reflected by the partially reflective platelet-shaped magnetic or
magnetizable pigment particles and collected by the imager at
corresponding viewing angle .theta., storing the calculated average
intensities of the reflected light and corresponding viewing angles
to obtain a reflected light intensity curve I(.theta.), comparing
the stored reflected light intensity curve I(.theta.) with a stored
reference reflected light intensity curve I.sub.ref(.theta.) for
said magnetically induced mark, and determining whether the
magnetically induced mark is genuine based on a result of the
comparison.
Inventors: |
DINOEV; Todor;
(Chavannes-pres-Renens, CH) ; DORIER; Jean-Luc;
(Bussigny, CH) ; HALASZ; Edmund; (Orbe, CH)
; LOGINOV; Evgeny; (Renens, CH) ; DESPLAND;
Claude-Alain; (Prilly, CH) ; CALLEGARI; Andrea;
(Chavannes-pres-Renens, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SICPA HOLDING SA |
Prilly |
|
CH |
|
|
Appl. No.: |
17/434704 |
Filed: |
February 10, 2020 |
PCT Filed: |
February 10, 2020 |
PCT NO: |
PCT/EP2020/053331 |
371 Date: |
August 27, 2021 |
International
Class: |
G06K 7/14 20060101
G06K007/14; G07D 7/12 20060101 G07D007/12 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2019 |
EP |
19160146.7 |
Claims
1. A method of authenticating a magnetically induced mark applied
on a substrate and comprising a zone with a plane layer of a
material including magnetically oriented partially reflective
platelet-shaped magnetic or magnetizable pigment particles, with a
portable device equipped with a light source operable to deliver
visible light, an imager, a processor and a memory, wherein the
zone of the magnetically induced mark comprises a first zone
including magnetically oriented partially reflective
platelet-shaped magnetic or magnetizable pigment particles, which
are tilted at a first angle to a first direction, the method
comprising: disposing the imager of the portable device facing the
zone of the magnetically induced mark; illuminating the first zone
of the magnetically induced mark with the light source and taking a
plurality of digital images of the illuminated first zone with the
imager being for each different digital image at a corresponding
distinct viewing angle .theta. with respect to said first zone, by
moving the imager above the magnetically induced mark in said first
direction of the orientation of the magnetic or magnetizable
pigment particles and parallel to the plane layer; for each digital
image of the illuminated first zone, calculating, with the
processor, a corresponding average intensity I of the light
reflected by the partially reflective platelet-shaped magnetic or
magnetizable pigment particles and collected by the imager at
corresponding viewing angle .theta.; storing the calculated average
intensities of the reflected light and corresponding viewing angles
to obtain a reflected light intensity curve I(.theta.); comparing
the stored reflected light intensity curve I(.theta.) with a stored
reference reflected light intensity curve I.sub.ref(.theta.) for
magnetically induced mark, and determining whether the magnetically
induced mark is genuine based on a result of the comparison.
2. The method according to claim 1, further comprising calculating
a rate of change of the reflected light intensity curve I(.theta.)
to determine an angular value and corresponding intensity peak
value of the curve; comparing the calculated angular value and the
intensity peak value with a stored reference angular value and
intensity peak value for said magnetically induced mark,
respectively, wherein determining whether the magnetically induced
mark is genuine is further based on a result of said
comparison.
3. The method according to claim 1, further comprising calculating
a variance of the reflected light intensity over said zone of the
magnetically induced mark from the acquired digital images;
comparing the calculated variance with a reference value of the
variance for said magnetically induced mark, wherein determining
whether the magnetically induced mark is genuine is further based
on a result of said comparison.
4. The method according to claim 1, further comprising reading a
geometrical reference pattern, the geometrical reference pattern at
least partially overlapping the zone of the magnetically induced
mark and being in the form of an encoded mark selected from encoded
alphanumeric data, one-dimensional barcode, two-dimensional
barcode, QR-code or datamatrix.
5. (canceled)
6. The method according to claim 1, wherein the zone of the
magnetically induced mark comprises a second zone with partially
reflective platelet-shaped magnetic or magnetizable pigment
particles tilted at a second angle to a second direction, different
from the first direction, and the method further comprises:
illuminating the second zone of the magnetically induced mark with
the light source and taking a plurality of digital images of the
illuminated second zone with the imager being for each different
digital image at a corresponding distinct viewing angle .theta.
with respect to said second zone, by moving the imager above the
magnetically induced mark in said second direction of the
orientation of the magnetic or magnetizable pigment particles and
parallel to the plane layer; for each digital image of the
illuminated second zone, calculating, with the processor, a
corresponding average intensity I of the light (8) reflected by the
partially reflective platelet-shaped magnetic or magnetizable
pigment particles and collected by the imager at corresponding
viewing angle .theta., storing the calculated average intensities
of the reflected light and corresponding viewing angles to obtain a
reflected light intensity curve I(.theta.), and comparing the
stored reflected light intensity curve I(.theta.) with a stored
reference reflected light intensity curve I.sub.ref(.theta.) for
magnetically induced mark, wherein determining whether the
magnetically induced mark is genuine is further based on a result
of said comparison.
7. The method according to claim 1, wherein the portable device is
a smartphone or tablet.
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. A non-transitory computer-readable medium comprising computer
code parts executable by a processor to cause a portable device
equipped with a light source operable to deliver visible light and
an imager, to perform the method of claim 1.
Description
TECHNICAL FIELD
[0001] The present application relates to a method for
authenticating a mark on a substrate, said mark printed with an ink
comprising magnetic or magnetizable pigment particles, and to a
portable device, preferably a smartphone, for implementing said
method.
BACKGROUND OF THE INVENTION
[0002] It is known in the art to use inks, compositions, coatings
or layers containing oriented magnetic or magnetizable pigment
particles, particularly also optically variable magnetic or
magnetizable pigment particles, for the production of security
elements in the form of magnetically induced mark, e.g. in the
field of security documents. Coatings or layers comprising oriented
magnetic or magnetizable pigment particles are disclosed for
example in U.S. Pat. Nos. 2,570,856; 3,676,273; 3,791,864;
5,630,877 and 5,364,689. Coatings or layers comprising oriented
magnetic color-shifting pigment particles, resulting in
particularly appealing optical effects, useful for the protection
of security documents, have been disclosed in WO 2002/090002 A2 and
WO 2005/002866 A1.
[0003] Magnetic or magnetizable pigment particles in printing inks
or coatings allow for the production of magnetically induced marks,
designs and/or patterns through the application of a corresponding
magnetic field, causing a local orientation of the magnetic or
magnetizable pigment particles in the unhardened coating, followed
by hardening the latter. The result is a fixed magnetically induced
mark, design or pattern. Materials and technologies for the
orientation of magnetic or magnetizable pigment particles in
coating compositions have been disclosed in U.S. Pat. Nos.
2,418,479; 2,570,856; 3,791,864, DE 2006848-A, U.S. Pat. Nos.
3,676,273, 5,364,689, 6,103,361, EP 0 406 667 B1; US 2002/0160194;
US 2004/70062297; US 2004/0009308; EP 0 710 508 A1; WO 2002/09002
A2; WO 2003/000801 A2; WO 2005/002866 A1; WO 2006/061301 A1; these
documents are incorporated herein by reference. In such a way,
magnetically induced marks which are highly resistant to
counterfeit can be produced. The so-obtained magnetically induced
marks produce an angular reflection profile that is substantially
asymmetric with respect to the normal to the substrate onto which
it is applied. This is unusual and differs from the classical
specular or Lambertian reflection/scattering behavior.
[0004] Security features, e.g. for security documents, can
generally be classified into "covert" security features on the one
hand, and "overt" security features on the other hand. The
protection provided by covert security features relies on the
concept that such features are difficult to detect, typically
requiring specialized equipment and knowledge for detection,
whereas "overt" security features rely on the concept of being
easily detectable with the unaided human senses, e.g. such features
may be visible and/or detectable via the tactile senses while still
being difficult to produce and/or to copy. Magnetically induced
marks are typically used as "overt" (or level 1) security features
which should allow direct and unambiguous authentication by the
human without any external device or tool. However, the
effectiveness of overt security features depends to a great extent
on their easy recognition as a security feature, because most
users, and particularly those having no prior knowledge of the
security features of a document or item secured therewith, will
only then actually perform a security check based on said security
feature if they have actual knowledge of their existence and
nature.
[0005] Even though the security level of magnetically induced marks
is high in terms of resistance to copy, the average consumer could
potentially be confused as to which exact effect should be observed
for a particular overt security element on a given product. In
particular, a flipping hologram (low security, low cost security
element) producing a similar pattern or logo may lead to
misinterpretation of authenticity by untrained consumer, as it will
also produce an angular dependent reflection pattern.
[0006] Many authentication methods using a smartphone have emerged
these recent years. Most of them rely on the imaging capabilities
of the smartphone camera to extract geometrical or topological
information below the human eye resolution, such as the one
disclosed in WO 0225599 A1, or beyond the capability of humans to
extract signals very close to the noise or to interpret weak
variations in the printed design colors or shapes, as disclosed in
WO 2013071960 A1. These methods have the advantage of extracting a
coded information for identification but require, on the other
hand, a high-resolution printing and/or magnifying optics attached
to the smartphone camera.
[0007] Other authentication methods applicable to low resolution
printed features have been developed which rely on a colorimetric
analysis of the security feature, as disclosed in US 2011190920,
based on holograms, or such as the SICPASMART.TM. disclosed in WO
2015052318 A1, which analyses the colorshifting properties of
optically variable patterns measured during an augmented reality
assisted azimuthal displacement of the smartphone around the
pattern. These methods rely on a smartphone camera movement with
respect to the mark which is complicated to achieve. Moreover, they
depend on external light illumination and hence are highly
sensitive to ambient light conditions (e.g. direct sunlight, dark
environment or highly chromatically unbalanced illumination).
[0008] Other authentication methods of features having angular
dependence of the reflected intensity have been proposed, such as
randomly oriented flakes, as disclosed in WO 2012 136902 A1 and US
20140224879, micro-mirror, diffractive features like holograms or
embossed 3D structures, as disclosed in WO 2015193152 A1 or US
2016378061. These are based on two-angular positions of the camera
to capture two images which are then analyzed.
[0009] It remains a challenge to control both the camera of the
smartphone and the sample illumination in order to obtain
reproducible measurements of the reflectivity of a security
feature. Smartphone cameras normally use automated exposure and
focusing algorithms which are adapted to typical camera usage (e.g.
landscape or portrait photographs) but such algorithms are not
adapted to imaging of highly reflective marks with magnetically
induced marks. The illumination of the security feature can
originate from the ambient lightning indoors or outdoors which is
in general unknown and difficult to control and can hamper reliable
detection of the specific security features of magnetically induced
mark such as angular reflectivity.
[0010] Accordingly, currently known smartphone-based authentication
techniques have a number of disadvantages including the following
ones: they require high resolution printing of fine structures;
and/or they rely on complex smartphone movements to reveal a color,
and/or they are not reliable due to limited available information
to accurately authenticate the exact angular dependence (for
example: methods where only two angular positions of the camera are
used in the prior art).
[0011] It is therefore desired to propose to the public, and
potentially also to the relevant inspectors, an improved, accurate
and reliable technical solution that is robust against ambient
light perturbations, does not rely on high resolution printing or
on complex movement of the smartphone and avoids a difficult to
control and non-intuitive tilted or azimuthal position or rotation
movement.
[0012] In particular, there is a need for an authentication method
and device, which can unambiguously distinguish a given
magnetically induced mark from another one or from another overt
security feature produced with other techniques and from an
imitation based on another technology that attempts to mimic or
simulate the effect but reproduces the security feature or logo
topology and has some angular dependence of the reflected
intensity.
[0013] It is therefore an object of the present invention to
provide a method of authenticating a magnetically induced mark used
as overt security feature printed or affixed on a substrate (such
as a label, product or document), using a portable device,
preferably a smartphone, in order to overcome the disadvantages of
the prior art.
[0014] It is a further object of the present invention to provide a
portable device, preferably a smartphone, for authenticating a
magnetically induced mark applied on a substrate, which is easy to
control, which has a good immunity to ambient light variability and
is highly discriminating against imitations and selective against
other angular dependent reflective marks.
[0015] It is a further object of the present invention to provide a
corresponding non-transitory computer-readable medium comprising
computer code parts or instructions executable by a processor to
cause a portable device equipped with a light source and an imager
to perform the method of authenticating as described herein.
SUMMARY OF THE INVENTION
[0016] According to one aspect, the present invention relates to a
method of authenticating a magnetically induced mark on a substrate
and comprising a zone with a plane layer of a material including
magnetically oriented partially reflective platelet-shaped magnetic
or magnetizable pigment particles, with a portable device equipped
with a light source operable to deliver visible light, an imager, a
processor and a memory, the method comprising:
[0017] disposing the imager of the portable device at a given
distance L over the zone of the magnetically induced mark;
[0018] illuminating the zone of the mark with the light source and
taking a plurality of digital images of the illuminated zone with
the imager being for each different digital image at a
corresponding distinct viewing angle .theta. with respect to said
zone, by moving the imager above the magnetically induced mark in a
direction parallel to the plane layer;
[0019] for each digital image, calculating, with the processor, a
corresponding average intensity I of the light reflected by the
pigments particles and collected by the imager at corresponding
viewing angle .theta.;
[0020] storing the calculated average intensities of the reflected
light and corresponding viewing angles to obtain a reflected light
intensity curve I(.theta.);
[0021] comparing the stored reflected light intensity curve
I(.theta.) with a stored reference reflected light intensity curve
Iref(.theta.) for said magnetically induced mark, and
[0022] determining whether the magnetically induced mark is genuine
based on a result of the comparison.
[0023] According to the aspect of the present invention, the imager
of the portable device is a camera, preferably, a smartphone
camera. In particular, the method takes advantage of the
geometrical arrangement of the smartphone camera and of its
built-in flash light which allows to selectively obtain reflection
of the flash light by the partially reflective platelet-shaped
magnetic or magnetizable pigment particles to the camera for a
specific position of the smartphone body. This position is
pre-determined by the knowledge and the control of the precise
particles' orientation angle, the knowledge of the camera
magnification and flash to camera distance and a prescribed camera
to mark distance.
[0024] In this way, a magnetically induced mark with a given
partially reflective platelet-shaped magnetic or magnetizable
pigment particles orientation angle can be distinguished with
accuracy from another mark with different particles' orientation
angle or marks producing similar effect, based on holographic films
or micro-mirror-based designs, for example. The use of the flash
illumination with well-known position in respect to the camera
decreases the influence of ambient illumination on the measurement
and increase the accuracy of the authentication. Further, a
suitable graphical user interface provides guidance to the user,
such as a target on the smartphone display, to position accurately
the smartphone at the correct location. A sequence of images of the
magnetically induced mark is then acquired with the flash light on,
while moving the smartphone parallel to the plane of the mark at a
prescribed distance. This image sequence is then analyzed by image
processing algorithms to extract reflective area from the mark or
local intensity pattern that contains said mark or a part of it.
For example, the image processing algorithms comprise the
extraction of intensity values from at least one predetermined area
(zone) of the images corresponding to specific designs of the
magnetically induced mark where the reflected intensity from the
partially reflective platelet-shaped magnetic or magnetizable
pigment particles is expected, or not for a given security image
design and position of the smartphone with respect to the image.
Criteria on the intensity value (level) of these zones as a
function of the position (and hence of the viewing angles) are used
to determine if the magnetically induced mark is authentic or not.
In one embodiment, the stored reflected light intensity curve
I(.theta.) is compared with a stored reference reflected light
intensity curve I.sub.ref(.theta.) for said image, and determining
whether the magnetically induced mark is genuine is based on a
result of the comparison, i.e. matching of curves within a given
tolerance criterion. Preferably, the reference reflected light
intensity curve I.sub.ref(.theta.) for said magnetically induced
mark is stored in the memory of the portable device or on the
remote server connectable to the portable device via any
communication means.
[0025] In a further aspect of the present invention, the method
comprises calculating a rate of change of the reflected light
intensity curve I(.theta.) to determine an angular value and
corresponding value of an intensity peak of the curve; comparing
respectively the calculated angular value and the intensity peak
value with a stored reference angular value and intensity peak
value for said magnetically induced mark. In this case, determining
whether the magnetically induced mark is genuine is further based
on a result of said comparison. Preferably, the reference angular
value and intensity peak value for said magnetically induced mark
are stored in the memory of the portable device or on the remote
server connectable to the portable device via any communication
means.
[0026] In other words, a reflection intensity profile can be
extracted as a function of the position (equivalent to angular
variation), it can be transformed to angular reflectance profile
which contains additional specific information that could be used
as authentication criteria (such as the profile width, peak
position, skew, asymmetry, inflection point(s) and other features).
The profile can be fed to a machine learning algorithm (e.g.
decision trees) to define rules for authentication that use
features in the profiles specific to magnetically induced
marks.
[0027] In a further aspect of the present invention, the method
further comprising calculating a variance of the reflected light
intensity over said zone of the magnetically induced mark from the
acquired digital images, comparing the calculated variance with a
reference value of the variance for said image, wherein determining
whether the magnetically induced mark is genuine is further based
on a result of said comparison. Preferably, the reference value of
the variance for said magnetically induced mark is stored in the
memory of the portable device or on the remote server connectable
to the portable device via any communication means.
[0028] Some reference background printing area that produce
Lambertian (symmetrical) reflection/scattering behavior, could also
be used to make intensity corrections and account for potential
irradiation non-uniformity, variations of illumination due variable
distance to sample, or variations in the image acquisition
parameters (such as gain or exposure time).
[0029] A geometrical reference pattern of known shape and
dimensions can be printed nearby or over the partially reflective
platelet-shaped magnetic or magnetizable pigment particles' image
to allow finding the magnetically induced mark on the substrate, to
do perspective correction, and to correct small variations in the
smartphone distance or tilts in respect to the substrate during a
scanning.
[0030] Accordingly, the method further comprises reading the
geometrical reference pattern, which at least partially overlapping
the zone of the magnetically induced mark and being in the form of
an encoded mark such as an encoded alphanumeric data,
one-dimensional barcode, two-dimensional barcode, QR-code or
datamatrix. This, in addition, allows identification of the
security mark for traceability purposes. The geometrical reference
pattern becomes fully readable only at a certain angular value
corresponding to non-specular reflection of illumination light so
that the zone appears as a uniform background, thus allowing the
device to decode the pattern.
[0031] According to one embodiment, at least one zone of the
magnetically induced mark comprises magnetically oriented partially
reflective platelet-shaped magnetic or magnetizable pigment
particles, which are co-parallel. Said zone thus represents an
overt security feature which produces a reflection intensity
profile that is substantially asymmetric with respect to the normal
to the substrate. This orientation pattern is known as
Venetian-blind effects, wherein the platelet-shaped magnetic or
magnetizable pigment particles have their magnetic axis parallel to
each other and parallel to a plane, wherein said plane is not
parallel to the substrate onto which said particles are applied. In
particular, optical effects wherein the partially reflective
platelet-shaped magnetic or magnetizable pigment particles are
parallel to each other and have a substantially the same elevation
angle of the pigment particle planes of at least 30.degree. with
respect to the plane of the substrate onto which the particles are
applied. Methods for producing Venetian-blind effects are disclosed
for example in U.S. Pat. No. 8,025,952 and EP 1 819 525 B1
[0032] Alternatively, or in addition, the magnetically oriented
mark comprises a first zone including magnetically oriented
partially reflective platelet-shaped magnetic or magnetizable
pigment particles, which are co-parallel in one first direction,
and a second zone with partially reflective platelet-shaped
magnetic or magnetizable pigment particles oriented in a second
direction, different from the first direction. The effects obtained
with this orientation pattern are known as flip-flop effects,
wherein the mark includes a first portion and a second portion
separated by a transition, wherein the particles are aligned
parallel to a first plane in the first portion and particles in the
second portion are aligned parallel to a second plane. Methods for
producing flip-flop effects are disclosed for example in EP 1 819
525 B1 and EP 1 819 525 B1. In this case, preferably, image
processing algorithms comprise the extraction of intensity values
from the two predetermined zones of the magnetically induced mark
as a function of the position of the image with respect to the
smartphone during the image (e.g. video) sequence. In particular
the rate of intensity variance from each of the two zones of the
magnetically induced mark as a function of the position of the
image is extracted.
[0033] In another aspect, the present invention provides a portable
device for authenticating a magnetically induced mark on a
substrate and comprising a zone with a plane layer of a material
including oriented partially reflective platelet-shaped magnetic or
magnetizable pigment particles, said device comprising:
[0034] a light source operable to deliver visible light and
illuminating the zone of the magnetically induced mark, an imager
operable to take a plurality of digital images of the illuminated
zone, for each different image at a corresponding distinct viewing
angle .theta. with respect to said zone, while moving above the
magnetically induced mark in a direction substantially parallel to
the plane layer,
[0035] a memory for storing the calculated average intensities of
the reflected light and corresponding viewing angles to obtain a
reflected light intensity curve I(.theta.), and
[0036] a processor operable to compare the stored reflected light
intensity curve I(.theta.) with a stored reference reflected light
intensity curve I.sub.ref(.theta.) for said mark, and determining
whether the mark is genuine based on a result of the
comparison.
[0037] In a further aspect of the present invention, the processor
is operable to calculate a rate of the change of the reflected
light intensity curve I(.theta.) to determine an angular value and
corresponding value of an intensity peak of the curve, to compare
the calculated angular value and the intensity peak with a stored
reference angular value and intensity peak value for said mark,
respectively, and to further base the decision whether the
magnetically induced mark is genuine on a result of said
comparison.
[0038] In a further aspect of the present invention, the processor
is operable to calculate a variance of the reflected light
intensity over said zone of the magnetically induced from the
acquired digital images, to compare the calculated variance with a
reference value of the variance for said mark, and to further base
the decision whether the magnetically induced mark is genuine on a
result of said comparison.
[0039] In a further aspect of the present invention, the device is
further operable to read a geometrical reference pattern, the
geometrical reference pattern at least partially overlapping the
zone of the magnetically induced and being in the form of an
encoded mark selected from encoded alphanumeric data,
one-dimensional barcode, two-dimensional barcode, QR-code or
datamatrix.
[0040] In a further aspect of the present invention, the portable
device is a smartphone or tablet.
[0041] In another aspect, the present invention provides a
non-transitory computer-readable medium comprising computer code
parts or instructions executable by a processor to cause a portable
device equipped with a light source operable to deliver visible
light and an imager, to perform the method of authenticating a mark
as described herein.
[0042] The present invention will be described more fully
hereinafter with reference to the accompanying drawings, in which
prominent aspects and features of the invention, which are no way
limiting, are illustrated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1 is a schematic illustration of detecting magnetically
oriented partially reflective platelet-shaped magnetic or
magnetizable pigment particles of a magnetically induced mark by
the smartphone due to particles reflection (or not) depending on
its position relative to the mark.
[0044] FIG. 2 is an example of a measurement setup with the
smartphone and a sample that is scanned in a plane parallel to the
smartphone and at fixed distance from the smartphone.
[0045] FIG. 3 illustrates the position of the magnetically induced
mark in the set of images and an angle of illumination/observation
for known smartphone to sample distance with graphical
representation of intensity profile.
[0046] FIG. 4 illustrates intensity and relative intensity profiles
of a magnetically induced mark extracted from sequence of
images.
[0047] FIG. 5 is a schematic illustration of a magnetically induced
mark with magnetically oriented partially reflective
platelet-shaped magnetic or magnetizable pigment particles in two
opposite directions.
[0048] FIG. 6 illustrates a particular printing design of one
embodiment of the invention which contains magnetically oriented
partially reflective platelet-shaped magnetic or magnetizable
pigment particles at two different orientations in different areas
of the magnetically induced mark (these two areas could also be at
least partially overlapping).
[0049] FIG. 7 illustrates a particular printing design of one
embodiment of the invention which contains magnetically oriented
partially reflective platelet-shaped magnetic or magnetizable
pigment particles at two different orientations in different areas
of the magnetically induced.
[0050] FIG. 8 is a schematic illustration of the smartphone
positions over a magnetically induced mark with two different
partially reflective platelet-shaped magnetic or magnetizable
pigment particles orientations as shown in FIG. 6 or FIG. 7, along
with the obtained image frames in these two positions.
[0051] FIG. 9 is a schematic representation of the effect of a
90.degree. rotation of the magnetically induced mark, or of the
smartphone in the plane of the mark, and a guiding target on the
screen.
[0052] FIG. 10 is a schematic representation of a magnetically
induced mark with magnetically oriented partially reflective
platelet-shaped magnetic or magnetizable pigment particles in E
direction (particles 1) and another class of particles (particles
2) oriented in S direction, at 90.degree. with respect to particles
1.
[0053] FIG. 11 is a graphical representation of an intensity
profile, its first derivative and second derivative vs the
position.
[0054] FIG. 12 is a graphical representation of an intensity
cross-section of the magnetically induced mark at one specific
position in respect to the smartphone showing individual partially
reflective platelet-shaped magnetic or magnetizable pigment
particles reflections.
[0055] FIG. 13 is a graphical representation of a profiles of the
relative intensity and of the variance of the intensity as function
of position of the magnetically induced mark in the set of images
showing similar behavior of relative intensity and variance.
[0056] FIG. 14 is a graphical representation of the intensity
profiles of various marks. The magnetically induced mark profile
clearly shows a significant difference with other marks by its
asymmetry with respect to the axis. Relative intensity profile A
relates to the magnetically induced mark, relative intensity
profile B is a colorshifting pattern made of non-magnetic
colorshifting platelet-shaped pigment particles, relative intensity
profile C is a pattern made of an ink comprising silver metal
particles, and the intensity profile D relates to a mere paper.
[0057] FIG. 15 illustrates examples of relative intensity and
variance profiles for various types of marks containing partially
reflective platelet-shaped magnetic or magnetizable pigment
particles, including magnetically induced marks, holograms and
micro-mirrors.
[0058] FIG. 16 illustrates various embodiments of the magnetically
induced marks.
[0059] FIG. 17 illustrates various features integrating a
magnetically induced mark with a QR code.
DETAILED DESCRIPTION
[0060] In the following, the reference will be made to the Figures
in describing various embodiments of the disclosure. This
description serves to better understand the concept of the
embodiments of the disclosure and points out certain preferable
modifications of the general concept.
[0061] It should be noted that the key advantages of the present
invention require some specificities of the magnetically induced
marks in order to be authenticated robustly and reliably,
namely:
[0062] A sharp angular dependence of local reflectivity should be
present;
[0063] The angular dependence should be azimuthally asymmetric with
respect to the normal to the mark axis;
[0064] The angular dependence should be well controllable by the
marking process and is determined by the co-parallel alignment of
the reflecting elements;
[0065] The background and mark surrounding should also be
controlled.
[0066] These requirements may be satisfied by several candidates of
security features used in the art as overt features in various
application of security printing, for banknotes, labels and tax
stamps, or secure documents, like passports, checks or credit
cards. The main examples of these candidates are:
[0067] (A) magnetically induced marks comprising oriented partially
reflective platelet-shaped magnetic or magnetizable pigment
particles;
[0068] (B) arrangements of micro-mirrors embossed onto metallic
substrates or films;
[0069] (C) arrangements of micro-lenses in an array with masks over
a reflective pattern;
[0070] (D) diffractive structures such as holographic foils or
embossed diffractive structures.
[0071] In contrast to needle-shaped pigment particles which can be
considered as one-dimensional particles, platelet-shaped pigment
particles are two-dimensional particles due to the large aspect
ratio of their dimensions. A platelet-shaped pigment particle can
be considered as a two-dimensional structure wherein the dimensions
X and Y are substantially larger than dimension Z. Platelet-shaped
pigment particles are also referred in the art as oblate particles
or flakes. Such pigment particles may be described with a main axis
X corresponding to the longest dimension crossing the pigment
particle and a second axis Y perpendicular to X which also lies
within said pigment particles. The magnetically induced marks
described herein comprise oriented partially reflective
platelet-shaped magnetic or magnetizable pigment particles that,
due to their shape, have non-isotropic reflectivity. As used
herein, the term "non-isotropic reflectivity" denotes that the
proportion of incident radiation from a first angle that is
reflected by a particle into a certain (viewing) direction (a
second angle) is a function of the orientation of the particles,
i.e. that a change of the orientation of the particle with respect
to the first angle can lead to a different magnitude of the
reflection to the viewing direction. Preferably, the partially
reflective platelet-shaped magnetic or magnetizable pigment
particles described herein have a non-isotropic reflectivity with
respect to incident electromagnetic radiation in some parts or in
the complete wavelength range of from about 200 to about 2500 nm,
more preferably from about 400 to about 700 nm, such that a change
of the particle's orientation results in a change of reflection by
that particle into a certain direction. Thus, even if the intrinsic
reflectivity per unit surface area (e.g. per .mu.m.sup.2) is
uniform across the whole surface of platelet-shaped particle, due
to its shape, the reflectivity of the particle is non-isotropic as
the visible area of the particle depends on the direction from
which it is viewed. As known by the man skilled in the art, the
partially reflective platelet-shaped magnetic or magnetizable
pigment particles described herein are different from conventional
pigments, in that said conventional pigment particles exhibit the
same color and reflectivity, independent of the particle
orientation, whereas the magnetic or magnetizable pigment particles
described herein exhibit either a reflection or a color, or both,
that depend on the particle orientation.
[0072] Examples of partially reflective platelet-shaped magnetic or
magnetizable pigment particles described herein include without
limitation pigment particles comprising a magnetic layer M made
from one or more of a magnetic metal such as cobalt (Co), iron
(Fe), gadolinium (Gd) or nickel (Ni); and a magnetic alloy of iron,
chromium, cobalt or nickel, wherein said platelet-shaped magnetic
or magnetizable pigment particles may be multilayered structures
comprising one or more additional layers. Preferably, the one or
more additional layers are layers A independently made from one or
more selected from the group consisting of metal fluorides such as
magnesium fluoride (MgF.sub.2), silicon oxide (SiO), silicon
dioxide (SiO.sub.2), titanium oxide (TiO.sub.2), and aluminum oxide
(Al.sub.2O.sub.3); or layers B independently made from one or more
selected from the group consisting of metals and metal alloys,
preferably selected from the group consisting of reflective metals
and reflective metal alloys, and more preferably selected from the
group consisting of aluminum (Al), chromium (Cr), and nickel (Ni),
and still more preferably aluminum (Al); or a combination of one or
more layers A such as those described hereabove and one or more
layers B such as those described hereabove. Typical examples of the
platelet-shaped magnetic or magnetizable pigment particles being
multilayered structures described hereabove include without
limitation A/M multilayer structures, A/M/A multilayer structures,
A/M/B multilayer structures, A/B/M/A multilayer structures, A/B/M/B
multilayer structures, A/B/M/B/A multilayer structures, B/M
multilayer structures, B/M/B multilayer structures, B/A/M/A
multilayer structures, B/A/M/B multilayer structures, B/A/M/B/A
multilayer structures, wherein the layers A, the magnetic layers M
and the layers B are chosen from those described hereabove.
[0073] According to one embodiment, at least a part of the
partially reflective platelet-shaped magnetic or magnetizable
pigment particles described herein are
dielectric/reflector/magnetic/reflector/dielectric multilayer
structures and
dielectric/reflector/dielectric/magnetic/reflector/dielectric
multilayer structures, wherein the reflector layers described
herein are independently and preferably made from one or more
selected from the group consisting of metals and metal alloys,
preferably selected from the group consisting of reflective metals
and reflective metal alloys, more preferably selected from the
group consisting of aluminum (Al), silver (Ag), copper (Cu), gold
(Au), platinum (Pt), tin (Sn), titanium (Ti), palladium (Pd),
rhodium (Rh), niobium (Nb), chromium (Cr), nickel (Ni), and alloys
thereof, even more preferably selected from the group consisting of
aluminum (Al), chromium (Cr), nickel (Ni) and alloys thereof, and
still more preferably aluminum (Al), wherein the dielectric layers
are independently and preferably made from one or more selected
from the group consisting of metal fluorides such as magnesium
fluoride (MgF.sub.2), aluminum fluoride (AlF.sub.3), cerium
fluoride (CeF.sub.3), lanthanum fluoride (LaF.sub.3), sodium
aluminum fluorides (e.g. Na.sub.3AlF.sub.6), neodymium fluoride
(NdF.sub.3), samarium fluoride (SmF.sub.3), barium fluoride
(BaF.sub.2), calcium fluoride (CaF.sub.2), lithium fluoride (LiF),
and metal oxides such as silicon oxide (SiO), silicon dioxide
(SiO.sub.2), titanium oxide (TiO.sub.2), aluminum oxide
(Al.sub.2O.sub.3), more preferably selected from the group
consisting of magnesium fluoride (MgF.sub.2) and silicon dioxide
(SiO.sub.2) and still more preferably magnesium fluoride
(MgF.sub.2), and the magnetic, the magnetic layer preferably
comprises nickel (Ni), iron (Fe), and/or cobalt (Co); and/or a
magnetic alloy comprising nickel (Ni), iron (Fe), chromium (Cr)
and/or cobalt (Co); and/or a magnetic oxide comprising nickel (Ni),
iron (Fe), chromium (Cr) and/or cobalt (Co). Alternatively, the
dielectric/reflector/magnetic/reflector/dielectric multilayer
structures described herein may be multilayer pigment particles
being considered as safe for human health and the environment,
wherein said the magnetic layer comprises a magnetic alloy having a
substantially nickel-free composition including about 40 wt-% to
about 90 wt-% iron, about 10 wt-% to about 50 wt-% chromium and
about 0 wt-% to about 30 wt-% aluminum. Particularly suitable
partially reflective platelet-shaped magnetic or magnetizable
pigment particles having the
dielectric/reflector/magnetic/reflector/dielectric multilayer
structure include without limitation
MgF.sub.2/Al/magnetic/Al/MgF.sub.2 wherein the magnetic layer
comprises iron, preferably comprises a magnetic alloy or mixture of
iron and chromium.
[0074] Alternatively, the partially reflective platelet-shaped
magnetic or magnetizable pigment particles described herein may be
partially reflective platelet-shaped colorshifting magnetic or
magnetizable pigment particles, in particular magnetic thin-film
interference pigment particles. Colorshifting elements (also
referred in the art as goniochromatic elements), such as for
example pigments particles, inks, coatings or layers are known in
the field of security printing exhibit a viewing-angle or
incidence-angle dependent color, and are used to protect security
documents against counterfeiting and/or illegal reproduction by
commonly available color scanning, printing and copying office
equipment.
[0075] Magnetic thin film interference pigment particles are known
to those skilled in the art and are disclosed e.g. in U.S. Pat. No.
4,838,648; WO 2002/073250 A2; EP 0 686 675 B1; WO 2003/000801 A2;
U.S. Pat. No. 6,838,166; WO 2007/131833 A1; EP 2 402 401 A1 and in
the documents cited therein. Preferably, the magnetic thin film
interference pigment particles comprise pigment particles having a
five-layer Fabry-Perot multilayer structure and/or pigment
particles having a six-layer Fabry-Perot multilayer structure
and/or pigment particles having a seven-layer Fabry-Perot
multilayer structure.
[0076] Preferred five-layer Fabry-Perot multilayer structures
consist of absorber/dielectric/reflector/dielectric/absorber
multilayer structures wherein the reflector and/or the absorber is
also a magnetic layer, preferably the reflector and/or the absorber
is a magnetic layer comprising nickel, iron and/or cobalt, and/or a
magnetic alloy comprising nickel, iron and/or cobalt and/or a
magnetic oxide comprising nickel (Ni), iron (Fe) and/or cobalt
(Co).
[0077] Preferred six-layer Fabry-Perot multilayer structures
consist of
absorber/dielectric/reflector/magnetic/dielectric/absorber
multilayer structures.
[0078] Preferred seven-layer Fabry Perot multilayer structures
consist of
absorber/dielectric/reflector/magnetic/reflector/dielectric/absorber
multilayer structures such as disclosed in U.S. Pat. No.
4,838,648.
[0079] Preferably, the reflector layers of the Fabry-Perot
multilayer structures described herein are independently made from
the one or more materials such as those described hereabove.
Preferably, the dielectric layers of the Fabry-Perot multilayer
structures are independently made from the one or more materials
such as those described hereabove
[0080] Preferably, the absorber layers are independently made from
one or more selected from the group consisting of aluminum (Al),
silver (Ag), copper (Cu), palladium (Pd), platinum (Pt), titanium
(Ti), vanadium (V), iron (Fe) tin (Sn), tungsten (W), molybdenum
(Mo), rhodium (Rh), Niobium (Nb), chromium (Cr), nickel (Ni), metal
oxides thereof, metal sulfides thereof, metal carbides thereof, and
metal alloys thereof, more preferably selected from the group
consisting of chromium (Cr), nickel (Ni), metal oxides thereof, and
metal alloys thereof, and still more preferably selected from the
group consisting of chromium (Cr), nickel (Ni), and metal alloys
thereof.
[0081] Preferably, the magnetic layer comprises nickel (Ni), iron
(Fe) and/or cobalt (Co); and/or a magnetic alloy comprising nickel
(Ni), iron (Fe) and/or cobalt (Co); and/or a magnetic oxide
comprising nickel (Ni), iron (Fe) and/or cobalt (Co). When magnetic
thin film interference pigment particles comprising a seven-layer
Fabry-Perot structure are preferred, it is particularly preferred
that the magnetic thin film interference pigment particles comprise
a seven-layer Fabry-Perot
absorber/dielectric/reflector/magnetic/reflector/dielectric/absorber
multilayer structure consisting of a
Cr/MgF.sub.2/Al/Ni/Al/MgF.sub.2/Cr multilayer structure.
[0082] The magnetic thin film interference pigment particles
described herein may be multilayer pigment particles being
considered as safe for human health and the environment and being
based for example on five-layer Fabry-Perot multilayer structures,
six-layer Fabry-Perot multilayer structures and seven-layer
Fabry-Perot multilayer structures, wherein said pigment particles
include one or more magnetic layers comprising a magnetic alloy
having a substantially nickel-free composition including about 40
wt-% to about 90 wt-% iron, about 10 wt-% to about 50 wt-% chromium
and about 0 wt-% to about 30 wt-% aluminum. Typical examples of
multilayer pigment particles being considered as safe for human
health and the environment can be found in EP 2 402 401 A1 which is
hereby incorporated by reference in its entirety.
[0083] The dielectric/reflector/magnetic/reflector/dielectric
multilayer structures described herein, the
absorber/dielectric/reflector/dielectric/absorber multilayer
structures described herein, the
absorber/dielectric/reflector/magnetic/dielectric/absorber
multilayer structures described herein and the
absorber/dielectric/reflector/magnetic/reflector/dielectridabsorber
multilayer structures described herein are typically manufactured
by a conventional deposition technique of the different required
layers onto a web. After deposition of the desired number of
layers, e.g. by physical vapor deposition (PVD), chemical vapor
deposition (CVD) or electrolytic deposition, the stack of layers is
removed from the web, either by dissolving a release layer in a
suitable solvent, or by stripping the material from the web. The
so-obtained material is then broken down to platelet-shaped
magnetic or magnetizable pigment particles which have to be further
processed by grinding, milling (such as for example jet milling
processes) or any suitable method so as to obtain pigment particles
of the required size. The resulting product consists of
platelet-shaped magnetic or magnetizable pigment particles with
broken edges, irregular shapes and different aspect ratios. Further
information on the preparation of suitable pigment particles can be
found e.g. in EP 1 710 756 A1 and EP 1 666 546 A1 which are hereby
incorporated by reference.
[0084] The magnetically induced marks described herein are prepared
by a process comprising the steps of: applying on a substrate a
coating composition comprising the partially reflective
platelet-shaped magnetic or magnetizable pigment particles
described herein; exposing the coating composition to the magnetic
field of a magnetic-field-generating device, thereby orienting at
least a part of partially reflective platelet-shaped magnetic or
magnetizable pigment particles; and hardening the coating
composition so as to fix the pigment particles in their adopted
positions and orientations. Detailed description of these steps
processed along with coating compositions can be found in the
following patent documents and the related references therein: US
2016176223 and US 2003170471.
[0085] The applying step described herein is carried out by a
printing process preferably selected from the group consisting of
screen printing, rotogravure printing and flexography printing.
These processes are well-known to the skilled man and are described
for example in Printing Technology, J. M. Adams and P. A. Dolin,
Delmar Thomson Learning, 5.sup.th Edition, p 293, 332, and 352.
[0086] Subsequently to, partially simultaneously or simultaneously
with the application of the coating composition on the substrate,
the partially reflective platelet-shaped magnetic or magnetizable
pigment particles are oriented by the use of an external magnetic
field for orienting them according to a desired orientation
pattern. The so-obtained orientation pattern may be any
pattern.
[0087] A large variety of magnetically induced marks can be
produced by various methods disclosed for example in U.S. Pat. No.
6,759,097, EP 2 165 774 A1 and EP 1 878 773 B1. Optical effects
known as rolling-bar effects may also be produced. Rolling-bar
effects show one or more contrasting bands which appear to move
("roll") as the image is tilted with respect to the viewing angle,
said optical effects are based on a specific orientation of
magnetic or magnetizable pigment particles, said pigment particles
being aligned in a curving fashion, either following a convex
curvature (also referred in the art as negative curved orientation)
or a concave curvature (also referred in the art as positive curved
orientation). Methods for producing rolling-bar effects are
disclosed for example in EP 2 263 806 A1, EP 1 674 282 B1, EP 2 263
807 A1, WO 2004/007095 A2 and WO 2012/104098 A1. Optical effects
known as moving-ring effects may also be produced. Moving-ring
effects consists of optically illusive images of objects such as
funnels, cones, bowls, circles, ellipses, and hemispheres that
appear to move in any x-y direction depending upon the angle of
tilt of said optical effect layer. Methods for producing
moving-ring effects are disclosed for example in EP 1 710 756 A1,
U.S. Pat. No. 8,343,615, EP 2 306 222 A1, EP 2 325 677 A2, WO
2011/092502 A2 and US 2013/084411.
[0088] Optical effects known as Venetian-blind effects may be
produced. Venetian-blind effects include a portion with pigment
particles having their magnetic axis parallel to each other and
parallel to a plane, wherein said plane is not parallel to the
identity document substrate. In particular, optical effects wherein
the pigment particles are parallel to each other and have a
positive elevation angle of the pigment particle planes with
respect to the plane of the substrate onto which the pigment
particles are applied. Venetian-blind effects include pigment
particles being oriented such that, along a specific direction of
observation, they give visibility to an underlying substrate
surface, such that indicia or other features present on or in the
substrate surface become apparent to the observer while they impede
the visibility along another direction of observation. Methods for
producing Venetian-blind effects are disclosed for example in U.S.
Pat. No. 8,025,952 and EP 1 819 525 B1.
[0089] Optical effects known as flip-flop effects (also referred in
the art as switching effect) are may be produced. Flip-flop effects
include a first portion and a second portion separated by a
transition, wherein the pigment particles are aligned parallel to a
first plane in the first portion and pigment particles in the
second portion are aligned parallel to a second plane. Methods for
producing flip-flop effects are disclosed for example in EP 1 819
525 B1 and EP 1 819 525 B1. Particular suitable orientation
patterns include the Venetian-blind effects and the flip-flop
effects described hereabove.
[0090] The processes for producing the magnetically induced marks
described herein comprise, partially simultaneously with step b) or
subsequently to step b), a step c) of hardening the coating
composition so as to fix the partially reflective platelet-shaped
magnetic or magnetizable pigment particles in their adopted
positions and orientations in a desired pattern to form the
magnetically induced marks, thereby transforming the coating
composition to a second state. By this fixing, a solid coating or
layer is formed. The term "hardening" refers to processes including
the drying or solidifying, reacting, curing, cross-linking or
polymerizing the binder components in the applied coating
composition, including an optionally present cross-linking agent,
an optionally present polymerization initiator, and optionally
present further additives, in such a manner that an essentially
solid material that adheres to the substrate surface is formed. As
mentioned herein, the hardening step may be performed by using
different means or processes depending on the materials comprised
in the coating composition that also comprises the partially
reflective platelet-shaped magnetic or magnetizable pigment
particles. The hardening step generally may be any step that
increases the viscosity of the coating composition such that a
substantially solid material adhering to the supporting surface is
formed. The hardening step may involve a physical process based on
the evaporation of a volatile component, such as a solvent, and/or
water evaporation (i.e. physical drying). Herein, hot air, infrared
or a combination of hot air and infrared may be used.
Alternatively, the hardening process may include a chemical
reaction, such as a curing, polymerizing or cross-linking of the
binder and optional initiator compounds and/or optional
cross-linking compounds comprised in the coating composition. Such
a chemical reaction may be initiated by heat or IR irradiation as
outlined above for the physical hardening processes, but may
preferably include the initiation of a chemical reaction by a
radiation mechanism including without limitation
Ultraviolet-Visible light radiation curing (hereafter referred as
UV-Vis curing) and electronic beam radiation curing (E-beam
curing); oxypolymerization (oxidative reticulation, typically
induced by a joint action of oxygen and one or more catalysts
preferably selected from the group consisting of cobalt-containing
catalysts, vanadium-containing catalysts, zirconium-containing
catalysts, bismuth-containing catalysts, and manganese-containing
catalysts); cross-linking reactions or any combination thereof.
Radiation curing is particularly preferred, and UV-Vis light
radiation curing is even more preferred, since these technologies
advantageously lead to very fast curing processes and hence
drastically decrease the preparation time of any document or
article comprising the magnetically induced marks described herein.
Moreover, radiation curing has the advantage of producing an almost
instantaneous increase in viscosity of the coating composition
after exposure to the curing radiation, thus minimizing any further
movement of the particles. In consequence, any loss of information
after the magnetic orientation step can essentially be avoided.
Particularly preferred is radiation-curing by photo-polymerization,
under the influence of actinic light having a wavelength component
in the UV or blue part of the electromagnetic spectrum (typically
200 nm to 650 nm; more preferably 200 nm to 420 nm). Equipment for
UV-visible-curing may comprise a high-power light-emitting-diode
(LED) lamp, or an arc discharge lamp, such as a medium-pressure
mercury arc (MPMA) or a metal-vapor arc lamp, as the source of the
actinic radiation.
[0091] Arrangements of micro-mirrors embossed onto metallic
substrates or films to produce angular dependent reflective pixels
that produce an angular varying image depending on the perspective
view as disclosed in WO 2017211450 A1 or in US 2017242263. These
security features might produce local angular dependent reflection,
although they are distinct by the fact that they cannot completely
vanish for any viewing angle. An additional difference resides in
the fact that the micro-mirror structures can be produced with high
resolution (30-50 micron pitch) to produce fine images. An
implementation that produces relatively large angular dependent
reflecting zones that could be produced with such structures that
could be authenticated using the method disclosed in the present
invention. However, these features can be distinguished from the
magnetically induced marks comprising the oriented partially
platelet-shaped magnetic or magnetizable pigment particles by the
spatial variance or entropy in the image, which is higher for the
magnetically induced marks than for micro-mirror-based marks.
[0092] Arrangements of micro-lenses in an array with masks over a
reflective pattern can also produce angular dependent varying
images or local reflections such as the one described in
US2007273143 (A1). By properly designing the locations of the
reflectors behind the masks, the micro lenses and the masks, one
could also obtain a sharp angular reflective pattern that could
potentially be authenticated using the method disclosed in the
present invention.
[0093] Diffractive structures such as holographic foils or embossed
diffractive structures could potentially also produce such angular
dependence, but with angular varying colors, which makes then
distinct from the previous examples. Such features are described
along with an authentication method using a smartphone camera at
two angular positions in WO 2015193152 A1 and in US 2016378061
A1.
[0094] In order to better understand the general concept of the
disclosure and to point out certain preferable modifications of the
general concept, authenticating a mark comprising partially
reflective platelet-shaped magnetic or magnetizable pigment
particles with a portable device will be further discussed in more
detail.
[0095] The present method of authenticating magnetically induced
marks 1 applied on a substrate 2 via portable device 3 is based on
the particular geometrical arrangement of an imager 4, e.g. a
smartphone camera, and a light source 5, i.e. a LED flash. On most
models of smartphones a camera aperture and the LED flash are
located side by side, with a separation of less than 15 mm.
Therefore, for a particular magnetic orientation of the
platelet-shaped magnetic or magnetizable pigment particles 6 in the
mark 1 with respect to the viewing direction, combined with a
suitable imaging distance, the geometric condition is fulfilled for
the light emitted by the flash, i.e. irradiation 7 to be back
reflected to the camera, i.e. reflection 8, whereas for other
orientations, the reflection is directed out of the camera. This is
illustrated in FIG. 1.
[0096] For example, if the magnetically induced mark has a majority
of platelet-shaped magnetic or magnetizable pigment particles
magnetically oriented at 15.degree. (angle .theta.) with respect to
the normal to the surface so that the incident flash light is
reflected predominantly at this direction and the mark will shine
when illuminated and observed at angles close to 15.degree. up to a
refractive index correction (angle .theta.) with respect to the
normal to the surface of the mark. Moreover, since the angular
field of view of the camera 4 is relatively large (typically
30.degree. half angle for a Samsung S3), and the flash divergence
angle is the same, the required angular orientation of the
platelet-shaped magnetic or magnetizable pigment particles with
respect to the camera to capture reflection can still be obtained
by keeping the smartphone body parallel to the substrate 2, as
shown in FIG. 2. The smartphone 3 is moved parallel to the
substrate 2 at a given distance, L, wherein, for example, L=80 mm,
while acquiring a set of images or a video sequence to be used for
authentication. Alternatively, the magnetically induced mark 1 is
also moved in respect to the smartphone 3 in a parallel plane.
[0097] FIG. 3 illustrates the positions x.sub.1' . . . x.sub.n' of
the magnetically induced mark in the set of images at a
corresponding viewing angle .theta. for the known smartphone to
sample distance L, with graphical representation of the lens 4'' of
camera 4 with effective focal length f and graphical representation
of intensity profile of a magnetically induced mark, wherein
I.sub.1 . . . I.sub.n are average intensities at corresponding
viewing angle .theta..
[0098] FIG. 4 illustrates intensity and relative intensity profiles
of a magnetically induced mark extracted from the sequence of
images. The first graph shows non-corrected intensity profile of
the magnetically induced mark zone which still represents the
effect. The intensity variation of the background (BKG) zone in
second graph shows the seemingly random phone auto-adjustments. The
third graph shows corrected magnetically induced mark relative
intensity profile which reveals the position dependent reflectivity
of the mark.
[0099] In particular, authenticating is performed by calculating,
for each digital image, a corresponding average intensity I of the
light reflected by the partially reflective platelet-shaped
magnetic or magnetizable pigment particles and collected by the
imager at corresponding viewing angle .theta.;
[0100] storing the calculated average intensities of the reflected
light and corresponding viewing angles to obtain a reflected light
intensity curve I(.theta.);
[0101] comparing the stored reflected light intensity curve
I(.theta.) with a stored reference reflected light intensity curve
I.sub.ref(.theta.) for said mark, and
[0102] determining whether the magnetically induced mark is genuine
based on a result of the comparison.
[0103] In one proposed embodiment of the invention, the
magnetically induced mark is designed so as to exhibit one or more
distinct zones, each with a specific orientation of the
platelet-shaped magnetic or magnetizable pigment particles. For
example, platelet-shaped magnetic or magnetizable pigment particles
oriented at 15.degree. to the W direction for the first zone and
particles oriented at 15.degree. to the E direction.
[0104] FIG. 5 schematically illustrates a magnetically induced mark
1 with magnetically oriented partially reflective platelet-shaped
magnetic or magnetizable pigment particles 6 and 6' in two opposite
directions. Some particles are tilted to West and some particles to
East direction thus reflecting the incident light in different
directions.
[0105] Examples of such a magnetically induced mark 1 are shown in
FIG. 6, illustrating the mark comprising platelet-shaped magnetic
or magnetizable pigment particles 6 (petals) and particles 6'
(disks)) and in FIG. 7 illustrating the mark comprising particles 6
(outer petals) and particles 6' (inner petals)). In this way
reflection can be obtained from particles of the first zone by
placing the mark at the right edge of the field of view of the
smartphone, whereas reflection of the other zone is obtained by
placing the mark at the left edge of the smartphone field of view.
This is further demonstrated in FIG. 8 which shows the smartphone
positions and the corresponding images obtained in these
positions.
[0106] In another embodiment of the invention, instead of moving
the smartphone in a linear direction parallel to the mark, a
90.degree. rotation of the mark itself, also parallel to its plane
can be made. FIG. 9 is a schematic representation of the effect of
a 90.degree. rotation of the mark, or of the smartphone in the
plane of the mark 1 on the substrate 2, and a guiding target 9 on
the screen. On the left image the central circle 10 is highly
reflective compared to the rest of the mark. On the right image the
central circle 10 is not reflective compared to the rest of the
mark and resembles the background.
[0107] This is explained by the fact that in one orientation the
partially reflective platelet-shaped magnetic or magnetizable
pigment particles are shining, whereas in the 90.degree. rotated
orientation, they are not, which is used as the authentication
criterion.
[0108] Another embodiment of the invention can make use of a
rotation of the smartphone at 90.degree. while keeping it parallel
to the mark instead of rotating the mark itself. In this case
either the first or the second zone of the mark will be reflecting
that can be used for authentication.
[0109] The exact location of the mark on the screen preview of the
smartphone and the distance of the smartphone to the mark together
define precisely the angle at which reflection can be obtained from
the platelet-shaped magnetic or magnetizable pigment particles. By
providing guiding targets 9 on the smartphone screen preview, the
user can easily position the smartphone laterally at the exact
location so that the exact angle can be obtained when the viewing
distance is also controlled.
[0110] The vertical position (viewing distance) can be guided by
the size of the target, which should fit the size of the mark at
correct distance, or by a second target to be aimed simultaneously
at a second mark or a barcode printed besides the magnetically
oriented design, or by a written message on the screen prescribing
the user to move closer or farther.
[0111] This makes the authentication method highly sensitive to the
exact platelet-shaped magnetic or magnetizable pigment particles
angle and hence allows a good discrimination of potential
imitations which would not reproduce the exact orientation.
[0112] FIG. 10 shows schematic representation of a mark with
magnetically oriented platelet-shaped magnetic or magnetizable
pigment particles 6 in E direction and another class of particles
6' oriented in S direction, at 90.degree. with respect to particles
6. In a similar manner as for the previous embodiments a sequence
of images can be recorded during the rotation of the mark with
respect to the smartphone.
[0113] Authentication is performed by analyzing reflected intensity
on the first and second zones of the mark in the two images
acquired at the two precise positions of the smartphone, thus
confirming the orientation angles. In addition, a sequence of
images can be acquired during the movement of the smartphone
between the two positions in a direction parallel to a plane layer
of the mark. Then the intensity from the two different zones with
platelet-shaped magnetic or magnetizable pigment particles oriented
in either direction is extracted and recorded as a function of the
position. Two intensity profiles are obtained which can be analyzed
in a similar way as described in FIG. 11 and/or FIGS. 12 and
13.
[0114] In this regard, FIG. 11 shows a graphical representation of
intensity profile, its first derivative and second derivative vs
the position. First derivative amplitude provides the rate of
intensity change and the position of the zero, gives the position
of the intensity maximum. The second derivative shows that the
intensity profile has two inflection points (inversion).
[0115] FIG. 12 provides a graphical representation of an intensity
cross-section of the mark at one specific position in respect to
the smartphone showing individual platelet-shaped magnetic or
magnetizable pigment particles reflections and high variance of the
intensity.
[0116] FIG. 13 shows profiles of the relative intensity and of the
variance of the intensity as function of position of magnetically
induced mark in the set of images showing similar behavior of
relative intensity and variance.
[0117] In a similar embodiment, a video sequence can be acquired
during a controlled lateral movement of the smartphone in the plane
parallel to the mark. This movement can be guided by augmented
reality, where a moving target is displayed on the smartphone
display and the user is encouraged to move the phone while
maintaining the mark within the target. In this way, the rate of
intensity change of the magnetically oriented shining
platelet-shaped magnetic or magnetizable pigment particles as a
function of the angle of view (calculated from the position of the
mark on the screen of the smartphone and the smartphone distance to
the mark) can be extracted from the video sequence. This rate of
intensity change is a strong authentication parameter, since it is
very sensitive to the exact angle at which the platelet-shaped
magnetic or magnetizable pigment particles are oriented. Rate of
intensity change can be obtained from the first derivative of the
profile as illustrated in FIG. 11. The second derivative can also
be used as a strong authentication parameter, by allowing to
determine the position of the inflection points in the profile.
State of the art magnetic orientation can provide angular position
of the platelet-shaped magnetic or magnetizable pigment particles
down to within +/-2 degrees. Even if a counterfeiter could produce
a mark with oriented platelet-shaped magnetic or magnetizable
pigment particles, it is not likely that the exact angle of
orientation could be obtained and the counterfeited mark can then
be detected as fake by this method with high accuracy.
[0118] It is also possible to use a video sequence to obtain a
relative intensity as function of angle of illumination of the mark
that corresponds to position of the mark on the screen during a
controlled lateral movement of the phone and in addition to obtain
the variance of the pixel intensity within the mark. Both profiles
of relative intensity and variance are dependent on the orientation
of the platelet-shaped magnetic or magnetizable pigment particles
in a magnetically induced mark. FIG. 14 and FIG. 15 show examples
of relative intensity profiles and variance profiles for various
marks. The examples include marks with inks containing non-oriented
and non-magnetic platelet-shaped magnetic or magnetizable pigment
particles, magnetically induced marks and finally marks with
holograms and micro mirrors as described above. In FIG. 15 the left
figures show relative intensity profiles (average intensity of the
observed secure mark relative to the e.g. average intensity of a
reference paper zone), and the right figures show profiles of the
variance of the intensity over the pixels of the image that include
the mark.
[0119] It is possible to see that marks with non-oriented
platelet-shaped magnetic or magnetizable pigment particles have
relative intensity profiles as well as variance profiles that are
centered and symmetrical. Contrary to these examples the
magnetically induced mark described herein show profiles with
strong skew. The intensity and variance peaks are shifted to one
side of the screen due to orientation of the platelet-shaped
magnetic or magnetizable pigment particles contained in the
security ink. Examples with holograms show significant difference
in the peak positions of the profiles for the three-color channels
which is not the case for any of the magnetically induced marks.
Finally, micro mirrors-based marks differ from the magnetically
induced marks by very low variance and off-peak high intensity,
even if the peak positions could resemble these of MOI marks.
[0120] This demonstrates that the proposed method allows to
differentiate accurately the different types of angular dependent
marks, and even to infer the angle of orientation of the
platelet-shaped magnetic or magnetizable pigment particles or
embossed structure, or micro-mirror. This is a clear demonstration
of the advantage over the methods described in the prior art that
capture images at only two angular positions.
[0121] The measurements shown in FIG. 15 are taken with a camera of
a smartphone Samsung S3 fixed at 80 mm from a sample of interest
moved parallel to the smartphone within the field-of-view of the
smartphone. The camera is set to macro auto focus, fixed white
balance, ISO setting and the sequence of pictures used for the
examples is taken manually. A video sequence can be used together
with function to adjust focus and exposure on object of interest
using object tracking function.
[0122] Each zone (patch) of interest, either a zone (patch) with a
security mark named signal zone (patch) or a paper zone (patch)
named a background zone (or background patch) is found with respect
to a QR code or other suitable geometrical mark on the label. The
positions on smartphone screen of the signal and background zones
(patches) are calculated including centers and areas with pixels
containing these zones (patches). An average intensity and variance
of all pixels within the zones (patches) is calculated for all
color channels (e.g. R, G, or B).
[0123] A relative intensity for each position of the signal and
background zones (patches) is calculated using the ratio of the
average pixel intensity in the signal zones (patches) to the
average pixel intensity in the background zones (patches) and this
is done for all color channels. The average pixel intensity for the
background zone (patch) is calculated always for the color channel
where the background zone (patch) has maximum intensity to assure
that the reference is using signal form channel where the paper has
maximum reflectance.
[0124] Using a reference to calculate the relative intensity makes
it possible to use the smartphone camera with automated setting of
the exposure time.
[0125] Further embodiments may comprise authentication algorithms
based on classifier or neural network-based machine learning which
are able to distinguish authentic intensity profiles (or other
measured or extracted features such as variance profile or image
entropy, etc.) from the ones that are not authentic.
[0126] As an example, the authentication of a mark can be
accomplished using machine learning. This operation then comprises
the three following steps of feature extraction, model training and
selection, and prediction. Regarding the step of feature
extraction, the imager returns a series of RGB images I(.theta.),
where .theta..sub.min.ltoreq..theta..ltoreq..theta..sub.max is the
scanning angle with respect to the normal to the mark. If
necessary, only a Region of Interest (Rol) around the mark may be
conserved by cropping the images. These images can be linearized
and converted to gray scale (as described in R. C. Gonzalez, T. E.
Woods, "Digital Image Processing", Fourth Edition, Pearsons, 2017).
However, separate processing of the color channels is also
possible.
[0127] For each image, one or several metric functions f(.theta.)
are calculated. A thorough description of image metrics applied to
images can be found in the above-mentioned book of R. C. Gonzales
and T. E. Woods. Metrics can either be computed on the image
intensity directly or on a transform, such as the Discrete Fourier
Transform (DFT) or the Discrete Wavelet Transform (DWT). Among the
useful metrics that can be used, we find the mean, the standard
deviation and the entropy. Depending on the metric used, we may
need to scale it by the average intensity of a reference adjacent
Rol (this operation allows compensating for the variable exposure
times of the imager and for any variations in the irradiation of
the mark).
[0128] For all measurements to have the same scale, metrics must be
estimated on a uniform sampling grid of angles. These angles must
be symmetric about the normal to the sample, for example
.theta.=[-20.degree., -18.degree., . . . ,0, . . . , +18.degree.,
+20.degree.]. We can denote this uniform grid as
.theta.=[.theta..sub.0 .theta..sub.1 . . . .theta..sub.D-1], where
D is the number of angles. Here, for example D=21. In practice,
scanning at uniformly-separated angles may not always be possible
and interpolation of the metrics may have to be performed. At the
end of the scanning procedure, we obtain the feature vector
x.sup.T=[f(.theta..sub.0) f(.theta..sub.1) . . .
f(.theta.0.sub.D-1)]=[x.sub.0 x.sub.1 . . . x.sub.D-1]. By further
performing N scans on different marks to account for their
variability, we build the data set X.sup.T=[x.sub.0 . . .
x.sub.N-1], with size D.times.N.
[0129] Regarding the step of model training and selection, general
machine learning techniques for classification and detection are
described in C. M. Bishop, "Pattern Recognition and Machine
Learning", Springer, 2009. Here, the authentication problem reduces
to distinguishing genuine feature vectors from fakes or attacks.
However, while genuine feature vectors are known and available, the
others are either unknown or rare. Thus, directly training a
two-class classifier is infeasible. As described in O. Mazhelis,
"One-Class Classifiers: A Review and Analysis of Suitability in the
Context of Mobile-Masquerader Detection," South African Computer
Journal, col. 36, pp. 29-48, 2006, authentication can be shown to
be equivalent to one-class classification. In this scenario,
classifier models only rely on genuine feature vectors to learn
their parameters and decision boundaries. Among these, Support
Vector Data Description (SVDD), v-Support Vector Classification
(v-SVC), Gaussian Mixture Models (GMM), and deep-learning models
such as Autoencoders are of practical interest. The selection of a
model is dictated by its performance during training and is also
constrained by its complexity. At equivalent performance, simpler
models are preferred. Prior to training the model, the data set X
is pre-processed as shown in the figure below and the following
steps are carried:
[0130] Sample cleanup. Defective samples such as those saturated or
with missing features are discarded.
[0131] Sample normalization. Feature vectors are normalized to unit
energy.
[0132] Feature standardization. Feature mean .mu.(.theta..sub.d)
and feature standard deviation .sigma.(.theta..sub.d) are estimated
and removed feature-wise.
[0133] Sample detrending. Low-order polynomial trends of fixed
order p are estimated on each sample and removed.
[0134] Feature reduction. Inter-feature correlations are removed,
and the dimensionality of the problem is reduced. Here, for example
the reduction can be from D=21 to K=3-5. Lower dimensionality
optimization problems converge faster and allow for easier
inspection. This step is accomplished through Principal Component
Analysis (PCA) (see the book of C. M. Bishop, "Pattern Recognition
and Machine Learning", Springer, 2009) that produces a vector
subspace V=[v.sub.0 . . . v.sub.K-1], with size D.times.K. After
PCA, we project the data set X onto subspace V, which results in
the reduced-feature data set X'.sup.T=[x'.sub.0 . . . x'.sub.N-1],
with size K.times.N. This data set is used for learning the
parameters .THETA. of the candidate one-class classification
models. Finally, the best candidate is retained for prediction.
[0135] Regarding the step of prediction, it performs on a data set
the operations of data cleanup, sample normalization, feature
standardization, detrending, subspace projection, computing of a
model decision function. Finally, after feature reduction by
subspace projection, the decision function of the classifier with
learned parameters is computed (see also I. GoodFellow, Y. Bengio,
A. Courville, "Deep Learning", MIT Press, 2016).
[0136] Even further embodiments may comprise a perspective
rectification to correct imperfect or varying alignment of the
imager with the plane of the mark. In addition, a spatial profile
stretching or compression due to camera to mark distance variations
can also be corrected by extracting the dimensions of a reference
mark contour or barcode in the images.
[0137] FIG. 16 illustrates various embodiments of the magnetically
induced marks: a) an orientation pattern where all the pigment
particles are co-parallel (referred as Venetian blind effect
described hereabove); b) "rolling-bar effect", where the pigment
particles's angle progressively increases from the mark center to
the edge; c) "flip-flop effect", where one area of the mark has
partially reflective platelet-shaped magnetic or magnetizable
pigment particles co-parallel with one angle, and another part of
the mark has pigment particles co-parallel with a different angle;
d) "hide and reveal" (referred as Venetian blind effect described
hereabove) where a background image or design is printed below the
magnetically induced marks and is either hidden by the
platelet-shaped magnetic or magnetizable pigment particles for a
given viewing angle or revealed for another viewing angle; e)
"flip-flop effect" superimposed where two different designs which
with co-parallel platelet-shaped magnetic or magnetizable pigment
particles are superimposed; f) "rotation" pattern where two zones,
each with co-parallel platelet-shaped magnetic or magnetizable
pigment particles having orientation tilted by 90.degree. from one
to another.
[0138] In an embodiment, a geometrical reference pattern in the
form of an encoded mark such as an encoded alphanumeric data,
one-dimensional barcode, two-dimensional barcode, QR-code or data
matrix may at least partially overlap the magnetically induced
mark. This, in addition, allows identification of the mark for
traceability purposes for example.
[0139] FIG. 17 illustrates exemplary various mark designs
integrating a magnetically induced mark 1 with a QR code 12 within
the background zone (background patch) 13, wherein the magnetically
induced mark 1 is close to QR code 12, or wherein the magnetically
induced mark 1 is inside QR code 12 or wherein the magnetically
induced mark 1 is over a static QR code 12. The QR code 12 could
either be static or dynamic (different for every mark 1) depending
on the application. The QR code 12 is used to locate efficiently
the mark and determine the magnification and allows to extract the
position in the field of view of the magnetically induced mark
during the sliding movement of the smartphone.
[0140] In this case, the QR code 12 is read at position where the
magnetically induced mark does not reflect to have enough contrast
not altered from magnetically induced mark back-reflection, and the
magnetically induced mark profile is measured and analyzed over the
black modules of the QR code to have maximum contrast between the
positions where the platelet-shaped magnetic or magnetizable
pigment particles are oriented to reflect back or not.
[0141] Preferably, the following method to measure the relative
intensity of the magnetically induced mark from an image that is
part of a video sequence may be used:
[0142] determining the center of the reference pattern (symbol) in
the image with index i;
[0143] calculating the position of the magnetically induced mark
zone in respect to the reference pattern (symbol);
[0144] measuring the average intensity I.sub.i of the magnetically
induced mark zone defined as average of intensity of all pixels
within the magnetically induced mark zone;
[0145] calculating the position of the reflectivity reference zone
referred to as background zone--BKG zone;
[0146] measuring the average intensity I.sub.BKG i of the BKG
zone;
[0147] calculating the relative intensity of the magnetically
induced mark zone I.sub.i=I.sub.i/I.sub.BKG i for all n images with
index i=1 . . . n from the video.
[0148] Using the geometrical reference pattern with pre-known
reflectivity (i.e. QR code quiet zone) which is placed in the
vicinity of the magnetically induced mark zone to measure the
relative magnetically induced mark patch intensity may further
reduce sensitivity to variable ambient illumination.
[0149] The present invention provides an improved, accurate and
reliable technical solution that is robust against ambient light
perturbations, does not rely on high resolution printing or on
complex movement of the smartphone and avoids a difficult to
control and non-intuitive tilted or azimuthal position or rotation
movement.
[0150] In fact, the present invention allows an easy to control
movement (i.e. parallel to the substrate) having a good immunity to
ambient light variability due to a light source, preferably a
smartphone flash, which dominates ambient light in most conditions.
Operating at close distance with the smartphone positioned parallel
to the substrate further reduces external light pollution by
shadowing the region of interest. The control for keeping the phone
in a given plane could be easily implemented by using, for example,
the smartphone's gyroscope. It could also be measured by the size
in the image and geometrical deformation (e.g. perspective) of the
observed label, mark or QR code. This is a key advantage of the
invention and also a substantial improvement compared to the prior
art.
[0151] Accordingly, the present invention does neither rely on high
resolution printing nor on complex movement of the smartphone and
makes use of the smartphone internal LED flash light which
increases its immunity to external (ambient) light conditions.
Moreover, because of the precise and low variance orientation of
the platelet-shaped magnetic or magnetizable pigment particles
(below +/-2.degree.), the invention is highly discriminating
against imitations and selective against other angular dependent
reflective marks.
[0152] Another advantage of the invention with respect to prior art
is provided by the detailed information obtained from the intensity
profile, which offers an enhanced security level in the
authentication. For example, the rate of intensity change increase
and drop is directly related to the homogeneity of platelet-shaped
magnetic or magnetizable pigment particles' orientation, which is
one of the most challenging features to obtain during the printing
process and hence the most difficult to forge. Moreover, the angle
of platelet-shaped magnetic or magnetizable pigment particles
orientation can be inferred from the angular reflection profile,
provided that a scale reference is present in the image (such as a
QR-code or any machine-readable code of known dimensions) and the
parameters of the camera are well known to calculate the
observation angle.
[0153] The above disclosed subject matter is to be considered
illustrative, and not restrictive, and serves to provide a better
understanding of the invention defined by the independent
claims.
* * * * *